Current x-ray techniques, including fluorescence, diffraction, small angle scattering, absorption refraction, and absorption spectroscopy, typically use an illumination beam with a single continuous cross section with a regular shape, such as a circular or oval spot. Such an illumination beam is not optimized to obtain high signal to noise ratio and/or high throughput using x-ray technique(s) on an object containing a single region of interest of arbitrary shape, or on a number of physically separated regions of similar or different shapes that may include periodic identical regions, such as semiconductor interconnects and through silicon vias (TSVs).
As illustrated in the fluorescence example of FIGS. 1A and 1B, when a conventional illumination beam 888-A with a single contiguous round cross section illuminates a region(s) of interest (ROI(s)) (illustrated in this example by a structure 840 with the shape of a cross) in an object 240 to be measured, the surrounding areas of the ROI 840 are also illuminated. As a result, x-rays collected by the x-ray detector 290 include not only x-rays 886 from the ROI 840 (shown in the figure as fluorescence x-rays by way of example) but also include a significant number of x-rays 885 generated from the surrounding illuminated areas. Signals from the detector may pass through a signal processor 292 for further analysis using a computer 295, and then displayed on a monitor 298. Because x-rays 885 generated from the surrounding areas are also detected with those from the ROI(s), a reduction of signal-to-noise ratio or difficulty in data analysis may result.
One approach to address this problem has been the use of an x-ray beam with a size smaller than the ROI, as illustrated in FIGS. 2A and 2B. A focused x-ray beam 888-B is created that illuminates a single spot 290-B within the ROI 840. The fluorescence x-rays 886-B that radiate from the spot 290-B are entirely from the ROI. However, because only a small portion of the ROI is illuminated with a small x-ray illumination beam, the generated x-rays 886-B will also be small. Attempts to increase the signal by increasing the integration time reduce the throughput, and in any case provide no information on anything but the illuminated spot. Collecting data for the entire ROI will require additionally scanning the spot over the region, further reducing the throughput.
There is therefore a need for a method and a system that can provide x-ray measurements of ROI(s) of interest in an object with high signal-to-noise ratios (S/N(s)) and/or high measurement throughput.